Study On High Toughness Polyimide Composites

As we all know, the toughness of composites can be improved by modifying the main chain structure of polyimide resins. In this study, a series of polyimide resins were synthesized by introducing the isomeric diamine and dianhydride to the main structure and endcapped with two types of end-capping reagents. The various prformance of resins have been studied and molding process of the resin casting and the composites were investigated. The resin casting and the corresponding composites were manufactured. In our investigation, the main conclusions are listed as follows:1. It is appropriate for the molding process as the matrix of composites, due to the low melting viscosity and the wide process window of the polyimide oligomer endcapped with nadic anhydride and acetylene.2. The decomposition temperature at5%weight loss for Polyimide oligomer endcapped with nadic anhydride (NA) and acetylene are more than450℃in air atmosphere after heat-crosslink, while the degradation temperature at5%weight loss for part resins is above500℃in nitrogen atmosphere. The temperature at5%weight loss for the iso-structural resins increases with the increasing molecular weight of resins.3. The flexural strength and the breaking elongation rate of the resin casting endcapped with nadic anhydride are more than100MPa and4%, respectively, indicating the excellent toughness. Moreover, the properties of the resin casting with iso-structure are modified with the increase in the molecular weight of the resins.4. The glass transition temperature (Tg) of the cured polyimide composites endcapped with nadic anhydride is more than300℃, which decreases with the molecular weight increases.5. The flexural strength of the carbon fiber reinforced NA-endcapped polyimide composites is more than1GPa, and its retention is more than40%at316℃. Further, the properties of the composites are improved with the increase of the molecular weight of the resins.